This invention relates to security systems, and particularly but not exclusively to vehicle entry security systems which utilise remote key-less entry schemes.
Remote Keyless Entry (RKE) is used widely in vehicles and other applications to allow a user to unlock a door or other opening without the need for a physical key to contact the door. Instead a button on the key fob is pressed by the user and a Radio-Frequency (RF) encrypted signal is sent to the vehicle. Upon decryption and verification of the signal the vehicle automatically unlocks the doors.
A further development of this system is the so-called xe2x80x98passivexe2x80x99 RKE, where the need for pressing a button is removed. Instead the user has a transponder (which may be incorporated in the key fob), and upon approaching the vehicle the user pulls the door handle as if the door were already unlocked. The vehicle sends out a Low Frequency (LF) signal with a range of 1 or 2 meters, and if the transponder is within this range it responds with a Ultra-High Frequency (UHF) encrypted signal which the vehicle receives. Upon decryption and verification of the received UHF signal the vehicle automatically unlocks the doors. The target time for this process is in the order of milliseconds, such that as the user continues to pull the door handle, the door opens.
A problem with both of the above systems is that there is a danger of unwanted interference from other UHF sources. In particular, if a number of vehicles in the vicinity of the user""s vehicle also have RKE and/or xe2x80x98passivexe2x80x99 RKE, there is a danger of unwanted interference from these other vehicles. This is of particular significance with respect to xe2x80x98passivexe2x80x99 RKE as the interference may cause the target time to be significantly lengthened as further attempts to transmit and receive the UHF signal take place, thus preventing the user from successfully opening the door with a single pull of the door handle. At best this is an inconvenience, but in bad weather or a potentially dangerous situation this could have more serious consequences.
This invention seeks to provide a security system and method which mitigate the above mentioned disadvantages.
According to a first aspect of the present invention there is provided a security system for a vehicle as claimed in claim 1.
According to a second aspect of the present invention there is provided a method of operating a security system for a vehicle as claimed in claim 2.
In this way a security system is provided in which the danger of unwanted interference from other UHF sources such as RKE systems of other vehicles is reduced. In particular the target time of passive RKE entry is kept to a minimum, with an improved probability that the user can successfully open the door with a single pull of the door handle.